Comparison of delignified coconuts waste and cactus for fuel-ethanol production by the simultaneous and semi-simultaneous saccharification and fermentation strategies

Fabiano Avelino Gonçalves,Héctor A Ruiz,Cleitiane Da Costa Nogueira,Everaldo Silvino Dos Santos,José A Teixeira,Gorete Ribeiro De Macedo

doi:10.1016/j.fuel.2014.04.021

Abstract

It is of the highest importance to study different alternatives/strategies as simultaneous (SSF) and semi-simultaneous (SSSF) saccharification and fermentation process, as well as the prospects of the utilization of lignocellulosic residues as raw materials for fuel-ethanol production. In the first part of this work, different raw materials (cactus (CAC), green coconut shell (GCS), mature coconut fibre (MCF) and mature coconut shell (MCS)) were pretreated by sequential alkaline hydrogen peroxide (Alk-H2O2)–sodium hydroxide (NaOH) process. The characterization of the obtained solids by FTIR, SEM, X-ray and crystallinity indexes confirmed the higher susceptibility of these pretreated materials to enzymatic action. These results were further confirmed by the corresponding glucose conversion yields – 68.44%, 70.20%, 76.21% and 74.50% for CAC, GCS, MCF and MCS, respectively. Subsequently, the comparison between SSF and SSSF using Saccharomyces cerevisiae, Pichia stipitis, Zymomonas mobilis and pretreated MCF (selected in the enzymatic hydrolysis step) was done, being shown that a short presaccharification step at 50°C for 8h in the SSSF had a positive effect on the overall ethanol yield, with an increase from 79.27–84.64% to 85.04–89.15%. In all the cases, the SSSF strategy allowed the obtention of higher ethanol concentrations than SSF.

Highlights

The use of biofuels, with emphasis on fuel-ethanol is an alternative to mitigate the pressure exerted by fossil fuels and their derivatives
The component present in higher amounts was cellulose with 38.33%, 32.88%, 31.6% and 30.47% for CAC, Green coconut shell (GCS), Mature coconut fibre (MCF) and Mature coconut shell (MCS), respectively, followed by hemicellulose and insoluble lignin, except for MCS, where lignin has a higher percentage than hemicellulose
The ethanol yield for S. cerevisiae PE2 was 84.64% (0.43 g ethanol/g sugar) and the volumetric productivity of ethanol 0.18 g/(L h), while for P. stipitis Y7124 and Z. mobilis B14023 the obtained values were 79.27% (0.40 g ethanol/g sugar) and 81.71% (0.42 g ethanol/g sugar) for ethanol yield and 0.19 g/(L h) and 0.17 g/(L h) for volumetric productivity of ethanol, respectively (Table 3). These results indicate that the glucose obtained from the enzymatic hydrolysis of pretreated MCF may be fermented to ethanol by S. cerevisiae PE2, P. stipitis Y7124 and Z. mobilis B14023, the kinetic profiles having a similar pattern for glucose consumption, with a rapid glucose consumption during the initial 24 h (Fig. 5A–C)

Summary

Introduction

The use of biofuels, with emphasis on fuel-ethanol is an alternative to mitigate the pressure exerted by fossil fuels and their derivatives. Fuel-ethanol production from corn, sugarcane and beet may be a problem in the near future due to the food competition in the use of these materials for bioenergy production [1]. Www.faostat.org.br), the world production of coconut in 2009 was about 55 million tons, mainly in the Philippines (36%), Indonesia (28%) and India (20%). Brazil is the fourth largest producer of coconut, with a production of about 3 million tons (5.5%) (http://www.ibge.gov.br). Associated with the large volume coconut production, large amounts of not used agroindustrial waste, suitable to be applied in fuel-ethanol production, are obtained. Just in Brazil, the production of CAC was 60,000 tons in 2009, mainly concentrated in the Northeast Region and was fully used in animal feed (http:// www.ibge.gov.br)

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